1. The Field of the Invention
The present invention relates generally to optoelectronic devices. More specifically, the present invention relates to optoelectronic devices with integrated variable optical attenuators.
2. The Relevant Technology
Computing, telecom and networking technology have transformed our world. As the amount of information communicated over networks has increased, high speed transmission has become ever more critical. Many high speed data transmission networks rely on optical transceivers and similar devices for facilitating transmission and reception of digital data embodied in the form of optical signals over optical fibers. Optical networks are thus found in a wide variety of high speed applications ranging from modest Local Area Networks to backbones that define a large portion of the infrastructure of the Internet.
In certain optical networks, such as dense wavelength division multiplexing (“DWDM”) networks, multiple optical signals from multiple optical light sources are multiplexed onto a single optical fiber. Each optical signal occupies a separate wavelength channel to avoid interfering with the other optical signals. As a result, it can be crucial to maintain each of the optical signals at a constant wavelength in a DWDM network.
Typically data transmission in such networks is implemented by way of a directly modulated laser (“DML”) that includes an optical light source, such as a laser diode. The optical light source emits light when current is passed through it, the intensity of the emitted light being a function of the magnitude of the current.
Alternately, data transmission can be implemented by way of an externally modulated laser (“EML”) that includes an optical light source and an electro-absorption (“EA”) modulator acting as a shutter. A constant current is applied to the optical light source to generate a light signal with constant intensity, and a modulation current applied to the EA modulator “opens” and “closes” the shutter.
Whether implementing a DML or an EML device, when the optical light source is first turned on, the wavelength of the emitted light signal may drift for a period of time until it stabilizes at a particular wavelength. This wavelength drift is referred to as wavelength transients and can also occur during channel selection of a tunable optical light source. Suppression of wavelength transients in a DWDM network may be highly desirable to prevent interference between optical signals.
In an EML device, wavelength transients suppression can be accomplished by simply “closing” the shutter during an initial turn-on phase or channel selection of the optical light source. Typically, however, EML devices are relatively expensive, large in size, and power hungry. Although DML devices are usually more affordable, smaller, and less power hungry than EML devices, they lack a shutter or any other wavelength transients suppression functionality.
In DWDM networks, it may also be important to maintain each of the optical signals at a particular output power. One method known in the art for changing the optical output power of an optical light source is to reduce the bias current of the optical light source. However, it is appreciated that this method changes the performance of the optical light source. Another method known in the art is to provide a separate variable optical attenuator (“VOA”) at the output of the EML or DML device. However, this method adds components, cost and complexity to the DWDM network.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.